Variable attenuator



Filed Jilly 22, 1937 fda/ara L. 60 kc m w JAJ 14 n n 1L m m w J- O U A a 2 l a a a O o H o O Patented July 25, 1939 UNITED STATES PATENT OFFICE 3 Claims.

My invention relates to improvements in variable, or step-by-step attenuators, also commonly known as potentiometers, T-pads, L-pads, H-pads, ladder-attenuators, etc., principally 5 used for volume control purposes in the radio industry, but also used for laboratory measurements of many kinds and in various types of instruments, and primarily consisting of an electrical network whose impedance characteristics are more or less constant and. whose loss characteristics may be varied in steps by a switching arrangement.

Heretofore all such devices have been of the rotary type in which the shaft extended through one end and with a knob placed on the shaft for direct manual operation. This type of attenuator, however, had many disadvantages, the most important one being that it was usually difficult to get to the switch contacts in the rear for cleaning, something which is necessary to insure satisfactory operation over a long period of time. A dial having numerals distributed around the greatest part of its periphery was usually necessary and had the disadvantage of being difficult to read except in the middle positions. In speech input equipment where it was often necessary to have six or eight, or even more, such attenuators operated by one operator the twisting of knobs became very tiresome.

39 An important object of my invention is therefore to provide an attenuator which may easily be cleaned from the front of the panel. A further object of my invention is to provide an attenuator having a vertical, linear dial which may very easily be read because all numerals are in the same vertical position on one line.

A still further object of the present invention is to eliminate fatigue in operating a number of attenuators over a period of time, and to facilitate w the observation at a glance of the position of any one unit by the location of its knob.

Further objects of the invention are to reduce noise due to thermal E. M. F.s created by the friction of switch contacts, and to reduce wear of 45 the contacts by reducing the distance of travel. Also to obtain easier operation, just by a flick of one finger, to obtain narrower construction whereby more units may be placed in a horizontal row with a given width of panel, and to obtain w longer switch blades and thus get better adjustment of spring tension and better wearing conditions. Other objects and advantages of the invention will be apparent during the course of the following description.

55 In the accompanying drawing, forming part of Figure 5 is a section along line 5-5 in Fig. 4, 10

Figure 6 is a section along line 6--6 in Figure 4,

Figure 7 is an enlarged portion of one insulating panel showing method of placing contacts,

Figure 8 is a plan view of a contact, and,

Figure 9 is a side view of same. II

In the drawing, wherein for the purpose of illustration, is shown a preferred embodiment of my invention, the numeral I0 designates a front cover plate, the knob II is secured to shaft I2 which is free to move in slot I 3. A pointer I 4 des- 20- ignates the loss on dial I5.

In the rear of the front cover I 0 is a combined dust cover and electrostatic shield I6 which encloses the attenuator proper with an opening for terminals I'I. I8 and may be removed as shown in Figure 4. The attenuator consists chiefly of two insulating panels I9 and 20, as shown in Figure 4, mounted together with spacers 2| and 22, and with posts 23, 24, and 26 for guiding the cover I6. shaft 21 is journalled in the two panels I9 and 20 and extending on one side with a hub 28 wherein is fastened the operating lever I 2. Contact points 29 are fastened securely in panel I9 and one end of these severally penetrate the panel I9 and are soldered to resistances 30 on the back of panel IS. The contact points 29 are placed close together due to the necessity of having many contacts in a short distance of travel of the switch.

To avoid drilling the holes in panel I9 too closely together, and thus weakening the insulating material, the holes 3| are staggered and the contact 29 is so designed as to be used in two ways, as shown in Figures 7, 8 and 9.

Fastened to shaft 21 between the panels I 9 and 20 is the switch member 32 which is preferably made from insulating material, and to this switch member 32 are fastened the switch blades 33 and 34. The blades 34 are riding on the row of contact points 29 as shown in Figure 5, while the blades 33 are riding on a collector ring 35 located on panel 20. By this arrangement the spring tension of the two sets of blades 33 and 34 is balanced and smooth operation is possible. In the illustrated case the circuit is either a so-called The cover I6 is held by a screw 25 the switches.

ill

ladder or a potentiometer, and the collector ring is either connected directly to one of the terminals H, or an impedance balancing resistor may be interposed if the circuit is a ladder. The switch blades 33 and 35 are fastened to gether mechanically and electrically by the rivets 36 for potentiometers and ladders, while for bridged T-pads the two sets of blades are insulated from one another. The construction shown is equally well suitable for bridged T and balanced ladder networks. To use these two circuits it is only necessary to place on panel 20 another row of contacts 29 similar to that on panel [9, and to place on each of the two panels either a separate collector ring similar to 35 or to use two separate so-called pig-tails for connecting the two sets of switch blades 33 and 34 to two separate fixed terminals. By the use of the two latter types of networks it is, of course, also necessary to place suitable resistors on panel 20 properly connected to the row of contacts to be placed there for this purpose. It is also obvious that more complicated circuits such as H and balanced H may be constructed by placing the required number of insulating panels together in a similar manner as illustrated for the bridged T and balanced ladder.

The front escutcheon i0 is made in such a manner that the slot l3 only opens to one side of panel 20 thus preventing dust from getting to The escutcheon l0 may be removed by unscrewing the mounting screws which go through the mounting holes 3? and clamp the unit to a suitable mounting. To remove the escutcheon I B it is also necessary to dismount the knob II from shaft [2. The attenuator unit proper is held to the front escutcheon It by two lugs 33 which are fastened to the spacers 22 and clamped against the top-edge of the insulating panels l9 and 20.

The operation of my invention is obvious from the description given supra. The operator merely pushes the knob H up or down, through the lever i2 this motion is transmitted to the switch member 32 and to the. switch blades 33 and 34 which serve to vary the lossof the circuit as previously described.

From the above description it is evident that there has been provided a new and useful device of unique characteristics which is well calculated to meet the various objects of the invention. It is to be understood that the form of my invention, herewith shown and described, is to be taken as a preferred example of the same,

and that various changes in the shape, size and arrangement of parts may be resorted to, without departing from the spirit of my invention, or the scope of the subjoined claims.

Having thus described my invention, I claim:

1. An attenuator of the character described comprising two triangularly shaped insulating panels; spacers for mounting said panels parallel to one another; a shaft journalled transversally through said panels near the apex of the triangle; a plurality of contact studs placed in an are on one of said insulating panels, said arc being arranged adjacent to the base of said triangularly shaped insulating panel; a selective switch member rotatable with said shaft and slidable over said arcuate contact studs; mounting means for fastening said attenuator to a rigid support; a removable front escutcheon and an operating lever with knob extending outwardly through a slot in said front escutcheon.

2. An attenuator of the character described comprising two triangularly shaped insulating panels, said panels being mounted in spaced relationship parallel to one another; a shaft journalled transversally through said panels near one corner of the triangle; a plurality of contact studs placed in an are on one of said insulating panels, said are being adjacent to one side of the triangle; a selective switch member rotatable with said shaft and slidable over said arcuate contact studs; mounting means for fastening said attenuator to a rigid support; a removable front escutcheon completely covering one side of said attenuator; an operating lever with knob extending outwardly through a slot in said front escutcheon, and shielding means surrounding said attenuator.

3. An attenuator of the character described comprising a plurality of triangularly shaped insulating panels, said panels being mounted in spaced relationship parallel to one another; a shaft journalled transversally through said panels near one corner of the triangle; a plurality of contact studs placed in arcs on said insulating panels, said arcs being adjacent to one side of the triangle; a selective switch member rotatable with said shaft and slidable over said arcuate contact studs; a removable front escutcheon covering the operating side of said attenuator; an operating lever with knob extending outwardly through a slot in said front escutcheon, and shielding means surrounding said attenuator.

EDWARD L. GOVE. 

